Electric motors are provided for a plethora of different use scenarios. One such scenario is a rotational movement of a motor to a mechanical end position. This scenario can e.g. be applicable in electronic locks, where control logic should be able to control the state of a lock to be either unlocked or locked.
When controlling a motor to a mechanical end position, a DC (Direct Current) motor can be used. A DC motor can be powered by mains power, battery power or otherwise stored electric power, e.g. from energy harvesting of mechanical motion.
Traditional motor control to reach a mechanical end position is to provide a preconfigured amount of energy to the motor which is sufficient to reach the end position. However, this energy can be excessive at early stages of the lifetime of the application, whereby more energy than needed is supplied. Excessive energy may also stress mechanical components or cause increased bumping, for which purpose additional mechanical components are added, thus increasing cost and space requirements.
WO 2008/101928A1 discloses a lock device adapted to unlock a lock by transferring a lock catch from a locking position to a releasing position. The device has an electric motor mechanically connected to an axle by means of at least one transmission means, and rotation of said axle actuates the lock catch. The device is characterized in that it comprises means for monitoring the current consumed by the electric motor. At the end the lock catch reaches its permanent stop position, which results in a rapid increase in current consumption. In order to measure the current, a resistor is connected in series with the motor. This causes some energy loss due to the voltage drop across the resistor.
US 2003/0100266 A1 discloses an access control system, a method and system for conserving battery life comprising an electronic control processor in a motor-driven locking subsystem for measuring samples of back electromotive force from a DC motor within the motor-driven locking subsystem. The samples of the back electromotive force are summed by the electronic control processor to form a comparison parameter value. The comparison parameter value is compared to a pre-determined threshold value to form a decision parameter. An action is taken by the electronic control processor in the motor-driven locking subsystem based on the decision parameter. This action comprises one of commanding the battery source in the motor-driven locking subsystem to increase the voltage level to the motor, generating a fail signal, or detecting and indicating a lock or unlock condition.
US2005/0127861 A1 discloses an actuator having an electric motor that generates a back emf. The actuator also includes a control system for controlling the speed of the electric motor. The control system includes a controller and circuitry for allowing the controller to sample the back emf of the motor. The controller uses the sampled back emf as feedback representative of motor speed for use in controlling the speed of the motor.